Carbon Sources and the Graphitization of Carbonaceous Matter in Precambrian Rocks of the Keivy Terrane (Kola Peninsula, Russia)

• Published in: Minerals
• Main Authors: Ekaterina Fomina, Evgeniy Kozlov, Kirill Lokhov, Olga Lokhova, Vladimir Bocharov
• Format: Article in Journal/Newspaper
• Language: English
• Published: MDPI AG 2019
• Subjects: graphitization; carbon isotopes; RSCM geothermometry; polyphase metamorphism; alkaline granites; Precambrian; Kola Peninsula; graphite; Mineralogy; QE351-399.2; kola peninsula
• Online Access: https://doi.org/10.3390/min9020094; https://doaj.org/article/184b2663861548a49d1b6056126ad5b1

The Precambrian rocks of the Keivy Terrane reveal five types of carbonaceous matter (CM): Fine-grained, flaky, nest, vein, and spherulitic. These types differ in their distribution character, carbon isotope composition, and graphitization temperatures calculated by the Raman spectra of carbonaceous material (RSCM) geothermometry. Supracrustal rocks of the Keivy Terrane contain extremely isotopically light (δ 13 C PDB = –43 ± 3‰) carbon. Presumably, its source was a methane–aqueous fluid. According to temperature calculations, this carbon matter and the host strata underwent at least two stages of metamorphism in the west of the Keivy Terrane and one stage in the east. The CM isotope signatures of several samples of kyanite schists (δ 13 C PDB = –33 ± 5‰) are close to those of oils and oil source rocks, and they indicate an additional carbon reservoir. Thus, in the Keivy territory, an oil-and-gas bearing basin has existed. Heavy carbon (δ 13 C PDB = −8 ± 3‰) precipitated from an aqueous CO 2 -rich fluid is derived from either the lower crust or the mantle. This fluid probably migrated from the Keivy alkaline granites into the surrounding rocks previously enriched with “methanogenic” carbon.